Role of thymidine for the activity of trimethoprim, sulfonamides and their combinations.

Thymidine levels in urines from 14 patients suffering from severe chronic urinary tract infection were determined microbiologically. The concentrations found were < 10 ng/ml to 33 ng/ml and these do not seem to be any different from the concentrations determined in healthy persons. Results from growth kinetic experiments support the assumption of low thymidine levels in the urines of these patients and in most cases trimethoprim or co-trimoxazole were seen to act in a bactericidal manner in these urine samples. Various aspects of the role of exogenous and endogenous thymidine for the activity and bactericidal effect of trimethoprim, sulfonamides and their combinations, their mutual synergism, the importance of thymine auxotrophs, the problem of thymidine availability and its role in testing media are discussed.